The UV+ has one DVI port on it and it only supports one monitor per UV+.  The FAQ in the UV+12 and 16 says 6 Max.  This was a typo in the manuals.  It was intended to be 6 UV+ on a system, not 6 monitors on a UV+.

The UV39 can support 2 monitors on one device, up to 3 devices and 6 monitors.